The long range goal of this investigation is to further our understanding of the role of calcium, as mediated by cytosolic calcium-binding proteins, in the regulation of excitation-coupled mechanisms in general, and in the regulation of contractile and secretory events in particular. The broad objectives outlined in this research proposal are: (a) to isolate the calcium-sensitive actomyosin complex from the adrenal medulla, to rigorously characterize the molecular components, and to elucidate the factors responsible for calcium sensitivity, (b) to investigate the role of the troponin-C-like calcium binding protein found in the adrenal medulla, calmodulin, in the regulation of cyclic nucleotide metabolism in this tissue, (c) to use isolated adrenomedullary secretory granules to investigate the role of contractile proteins, calcium ions and calcium binding proteins on both the calcium-stimulated release of catecholamines and the calcium-dependent aggregation of these chromaffin granules, and (d) to use the techniques of protein sequencing, chemical modification and protein fragmentation to identify specific amino acid residues or larger elements of structure with the calmodulin molecule which can be correlated with the specifically identified functional roles of myosin-kinase activation, cyclic nucleotide phosphodiesterase activation, adenylate cyclase activation, and myofibrillar actomyosin ATPase activation. In addition, both structural and functional studies will be carried out on a newly discovered calcium-dependent phosphodiesterase activator which copurified with carp muscle parvalbumin.